The present invention relates to the making of tools, and more particularly to a method of spray forming readily weldable metal deposits of low carbon steel.
Spray forming has become an accepted technique for producing steel prototype tooling (such as dies or molds) in a fraction of the time needed to make steel tooling conventionally. Spray forming techniques typically involve the following steps: (i) casting and solidifying a ceramic spraying pattern about a plastic master pattern of the tool to be produced; (ii) thermally spraying metallic particles onto a ceramic pattern; (iii) allowing the sprayed metallic particles to cool thereby forming a metal deposit having the general shape of the master pattern; and (iv) separating the metal deposit from the ceramic pattern.
The metallic particles being thermally sprayed onto the ceramic pattern typically consist of steel having a carbon content of about 0.8% by weight. The use of steel having a carbon content of about 0.8% by weight results in metal deposits which have good surface and structural characteristics. However, the deposits formed of carbon steel have a carbon content of about 0.4% to 0.8% by weight do not lend themselves to be easily weldable or machinable. Thus, when a tool (i.e., a die or mold) formed of a metal deposit made using steel having a carbon content of about 0.8% by weight cracks, or needs modifying to accommodate a design change, the tool is no longer useful and a brand new tool must be prepared since the tool is not easily weldable or machinable.
Accordingly, it would be desirable to provide a method of making a spray forming metal deposit which is readily weldable and machinable. Accordingly, it is an object of the present invention to provide a readily weldable and machinable metal deposit and a method of making the same.
The invention meets the above object and others by providing a method of spray forming a readily weldable and machinable metal deposit. The method comprises (a) providing a ceramic spray forming pattern; (b) heating the spray forming pattern to a sustained temperature sufficient to inhibit internal stress formation in carbon steel having a carbon content of less than about 0.3 weight percent deposited on the heated spray forming pattern; (c) spraying metallic particles onto the spray forming pattern while the spray forming pattern is heated to the sustained temperature, the metallic particles having a carbon content which is sufficient to result in metal particles having a carbon content of less than about 0.3 weight percent when deposited on the heated spray forming pattern; and (d) allowing the sprayed metallic particles to cool to form a metal deposit having a carbon content of less than about 0.3 weight percent.